1. Field of the Invention
The present invention relates to a sintered polycrystalline diamond composite for use in rock drilling, machining of wear resistant materials, and other operations which require the high abrasion resistance or wear resistance of a diamond surface. Specifically, this invention relates to such bodies that include a polycrystalline diamond layer attached to a cemented carbide substrate via processing at ultrahigh pressures and temperatures.
2. Description of the Art
It is well known in the art to form a polycrystalline diamond cutting element by sintering diamond particles into a compact using a high pressure, high temperature (HP/HT) press and a suitable catalyst sintering aid. Apparatus and techniques to accomplish the necessary sintering of the diamond particles are disclosed in U.S. Pat. No. 2,941,248 to Hall and U.S. Pat. No. 3,141,746 to DeLai. U.S. Pat. No. 3,745,623 Wentorf et al. teaches sintering of the diamond mass in conjunction with tungsten carbide to produce a composite compact (PDC) in which the diamond particles are bonded directly to each other and to a cemented carbide substrate.
To improve the abrasion characteristics of these cutters, very fine particle size diamond is used to make the sintered diamond body. Use of finer particle size diamond requires the use of higher pressures in order to obtain optimal sintering. The use of these higher pressures introduces higher internal stress into the finished PDC cutting element which has a negative affect on the impact resistance. One measurement of this internal stress is determined in the laboratory by a drop test well known in the art and is performed at room temperature. Room temperature impact resistance is not necessarily an accurate measure of how a PDC cutter will perform in the field. However, PDC's made at these higher pressures do often shatter or delaminate during bit manufacture or use. Brazing operations during bit assembly and high temperatures reached while drilling weaken the cutter as a result of the thermal expansion of the metal catalyst within the pore structure of the sintered diamond body overcoming the strength of the diamond to diamond bonds. Another factor for PDC is the strength of the bond between the diamond table and the substrate. When quenched from HPHT conditions to room pressure and temperature the substrate, with its a much higher thermal expansion coefficient than the diamond, places the diamond table into very high compression. In order to relieve the stress induced by this compressive force the PDC fractures or delaminates.
A method is needed to manufacture PDC cutting elements at higher pressures to improve the abrasion resistance without sacrificing the impact resistance due to high internal stress.